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Cliff Sadof, Extension Entomologist (Photos by Jeff Burbrink, Elkart County CES)
Every year during mid- to late April or early May, small green European pine sawflies strip the needles of from two needled pines before new needles are produced in the spring. Commonly affected trees include Mugo, Scotch and Austrian pine. Young larvae are dark green and difficult to see. Needles consumed by young larvae resemble slender brown straw. As damage accumulates, more straws become visible on branches. Late instar larvae grow to one inch and are dark green with a black head and black longitudinal stripes. After larvae become about 1" long, larvae pupate in brown pupal cells (1/2" long) that can be found along the trunk or on the ground. Adults emerge in early April. First chewed needles are visible in mid- to late April.
Sawfly larvae are easily killed by most broad spectrum insecticides, insect growth regulators, botanicals, or insecticidal soap or oil. Most effective control is achieved when pesticide is applied early in the season when sawflies are young. After sawflies are one inch long they stop feeding and construct a pupae. Applications of insecticide at this time are no longer needed.
Sawflies regularly suffer from a lethal virus-like disease that greatly reduces their number. If you notice larvae that are hanging limp from pine needles there is no need to apply an insecticide. This virus-like disease is not likely to be commercially available in the near future.
Plant and Pest Digital Library and Digitally Assisted Diagnosis, Purdue University, West Lafayette, Indiana.